Common Bottlenose Dolphins, Tursiops truncatus
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Description & Behavior
Bottlenose dolphins of the Genus Tursiops are at least three different species: Tursiops truncatus (Montagu, 1821), called common bottlenose dolphins, Tursiops aduncus (Ehrenberg, 1833), the Indo-Pacific or Indian Ocean bottlenose dolphins, and Tursiops australis, called the Burrunan dolphins. Bottlenose dolphins are the largest of the beaked dolphins weighing in at 150-200 kg. Head and body length is 175-400 cm, with males being much larger than females. Pectoral fin length is 30-50 cm, and dorsal fin height is approximately 23 cm. Width of the tail flukes is about 60 cm. The genus Tursiops is distinguished by a short, well-defined snout or beak which is about 8 cm long and apparently resembles the top of an old-fashioned gin bottle (hence the name). There are 20-28 sharp conical teeth on each side of each jaw, with each tooth about 1 cm in diameter. Tursiops have larger brains than those of humans and shows a high degree of "intelligence."
The beloved bottlenose dolphin is a distinctly social species that often travels in groups of up to 12 individuals, though occasionally they aggregate in groups of several hundred. Most populations do not migrate, but travel fairly widely to find food or locate waters of preferred temperature. They swim at speeds of approximately 19 kph.
T. truncatus displays a wide variety of vocalizations and is hypothesized to have a complex language. Researchers hope to eventually use this language to communicate meaningfully with dolphins. Each dolphin appears to have its own distinctive whistle used to communicate information on its identity, location, and condition to other dolphins. Dolphins also use click-like pulses produced by nasal sacs in the forehead for echolocation.
From the time of the early Greeks, it has often been claimed that dolphins will save humans from drowning or from shark attacks, although concrete evidence for these claims has not been found. Dolphins will, however, help other dolphins breathe at the surface when they are in distress. The mother-offspring bond is so strong in dolphins that females have often been observed holding stillborn or otherwise dead babies at the surface.
World Range & Habitat
Nearctic, Neotropical, Atlantic Ocean, Pacific Ocean: Common bottlenose dolphins, T. truncatus are found primarily in temperate and tropical waters of the Atlantic and Pacific Ocean and adjoining seas. In US waters, bottlenose dolphins range as far north as Cape Hatteras, NC in the summer and in the west to Point Conception, CA. They are found off the coasts of Hawaii and Florida year-round. T. aduncus is also common in the temperate and tropical waters of the Indian Ocean and adjoining seas, including the Red Sea.
Bottlenose dolphins are fond of warm, shallow inshore waters. They are commonly found in bays and lagoons as well as sometimes in the larger rivers. In certain areas it ranges as far offshore as the edge of the continental shelf.
Feeding Behavior (Ecology)
In the wild, bottlenose dolphins feed on squid, shrimp, and a wide variety of fishes such as eels. In some waters, bottlenose dolphins habitually follow shrimp boats to consume what the shrimpers discard or miss. They often hunt as a team, herding small fishes, such as menhaden, ahead of them and picking off the stragglers. They have been observed chasing fish onto mudflats and sliding out of the water to seize their prey. They generally consume approximately 6-7 kg of seafood daily.
Males fight viciously over females during the breeding season, and a hierarchy based on size is generally established among males. The beginning of the brief pair bond takes place when the male shows a preference for a particular female and remains with her for prolonged periods of time. The male often postures in front of the female with his back arched and also strokes, rubs, and nuzzles her. Mouthing, jaw clapping, and yelping are also part of precopulatory behavior. Courtship can sometimes be rather violent, with male and female bumping heads forcefully. Intromission is rapid (10 seconds, but may be repeated) and takes place underwater belly to belly when the female rolls over on her side, presenting her ventral (lower) surface to the male.
The height of sexual activity of the bottlenose dolphin is in March and April. In European waters, offspring are born in midsummer while births off the coast of Florida occur from February to May. The normal interval between calves is 2-3 years, but another offspring may be produced a year later if the first calf dies at birth. Gestation (pregnancy) is 12 months. Newborn calves are 98-126 cm long and weigh 9-11 kg. Lactation (nursing) lasts from 12-18 months, but young begin to eat solid food when less than 6 months old. Mother and calf often remain closely associated until the young is 4 or 5 years old. Females become sexually mature at 5-12 years of age, while males are mature at 9-13 years.
Conservation Status & Comments
Bottlenosed dolphins have been used since 1949 in shows in oceanariums that feature dolphins doing tricks to entertain the audience. They are easily trained to perform acrobatics, locate hidden objects and play with balls. They are also used widely in research work involving cetacean physiology, psychology and sociology. Dolphins have been hunted by people in many parts of the world for meat and products (such as fertilizer, body oil for cooking and illumination, and jaw oil used as a lubricant in fine machinery) made from dolphin parts.
Fishermen sometimes shoot bottlenose dolphins because they believe the dolphins are competing with them for fish and other desirable catch.
Protected under the Marine Mammal Protection Act of 1972, taking of dolphins in U.S. waters is only allowed with a special permit. Because of commercial fishing operations dating back to the late 1800s, bottlenose dolphin numbers were drastically reduced by the turn of the century. The U.S. National Marine Fisheries Service estimated that there were 3,000 to 10,000 bottlenose dolphins off the east coast of the United States in 1981. The biggest threat now to dolphin populations overall are pollution and drive hunts such as those illustrated in the movie The Cove though bycatch rates are still high in commercial fishing activities for tuna. Open ocean dolphins, like spinner dolphins, school with tuna and become trapped and then drown in the vast nets set by fishermen.
References & Further Research
Jefferson, T.A., S. Leatherwood, and M.A. Webber, FAO species identification guide, Marine mammals of the world, Rome, FAO. 1993. 320 p. 587 figs.
Milinkovitch, Michel C. and Lambert, Olivier. 2006. Cetacea. Whales, dolphins, and porpoises. Version 07 August 2006.
Harrison, R. and M.M. Brayden. 1988. Whales, Dolphins and Porpoises. Intercontinental Publishing Corporation, New York.
Lowery, G.H. Jr. 1974. The Mammals of Louisiana and Its Adjacent Waters. Kingsport Press, Inc., Knoxville, TN.
Nowak, R.M. and J.L. Paradiso. 1983. Walker's Mammals of the World. 4th edition. John Hopkins University Press, Baltimore, MD.
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